There are a number of different medical conditions in which the course of treatment involves the injection of cement into the hard tissue, the bone of the patient. One such procedure is a vertebroplasty procedure. In a vertebroplasty procedure bone cement is injected into a vertebra that was previously fractured. The procedure is performed to stabilize fractured vertebra. The procedure is performed to reduce the undesirable effects of the fracture. These effects are known to include, back pain, spinal deformity and loss of patient height.
In a vertebroplasty procedure and other procedures in which cement is injected into bone an assembly that consists of at least two cannulae is often employed to inject the cement. The first one of the cannula is an access cannula. The access cannula is used to define a portal from the outside environment, through soft tissue that surrounds the bone and into the bone into which the cement is to be injected. The assembly includes one additional cannula, referred to as a delivery cannula or cement cannula. The delivery cannula is dimensioned to be inserted into the lumen of the access cannula.
To actually deliver the bone cement the access cannula is first inserted into the patient. Often during the positioning process a pointed tip stylet is seated in the lumen of the access cannula. The tip of the stylet is the component of the assembly that pierces the tissue through which the cannula is inserted. The access cannula is positioned so the end of the cannula is positioned at the location in bone in which the cement is to be introduced. In some bone cement procedures a device is used to widen out space around the distal end of the access cannula. This is step is performed to ensure the presence of a void space into which the cement can flow. A previously filled delivery cannula is then seated in the access cannula. An obturator, a type of a plunger is then employed to force the bone cement out of the delivery cannula into the space into which the cement is to be introduced.
To minimize the trauma to the patient and to facilitate the precise control of the discharge of bone cement, both the access cannula and delivery cannula are relatively small in size. For example an access cannula often has an outer diameter of 5 mm or less. By extension that means that the inner diameter of the delivery cannula, the diameter of the lumen internal to the delivery cannula is 3.5 mm or less. This means that the volume of cement contained in any given filed delivery cannula is often 2 cm3 or less. Often a procedure in which it is necessary to inject bone cement into a patient requires a volume of cement that is greater than the volume contained in any one delivery cannula. This is why at the start of the procedure the practitioner has available two or more delivery cannula. Once the cement is discharged from one delivery cannula, the practitioner withdraws that cannula from the access cannula. A replacement delivery cannula filled with cement is then inserted into the cannula. Once the newly filled delivery cannula is in place, the part of the procedure in which the cement is actually injected into the bone can continue.
A problem during the cement injection procedure has been known to occur during the time period between the withdrawal of one delivery cannula from the access cannula and the insertion of a second access cannula. Specifically, during this time period, the access cannula, which is then empty, is known to fill with blood. This fluid is known to leak out of the proximal back end of the access cannula. To prevent this fluid leakage and the subsequent need to clean this fluid, the current practice is for the practitioner to, as soon as he/she removed the withdraws a delivery cannula, place a thumb or finger over the open proximal end of the cannula. This digit must be carefully positioned so as to not cause the movement of the access cannula. Having to hold the access cannula while putting away the empty delivery cannula and fitting a filled delivery cannula back into the access tube can make the removal and refitting of these cannulae an ergonomically awkward experience.